Arkose is typically grey to reddish in colour. The sand grains making up an arkose may range from fine to very coarse, but tend toward the coarser end of the scale. Fossils are rare in arkose, due to the depositional processes that form it, although bedding is frequently visible. Arkose is generally formed from the weathering of feldspar-rich igneous or metamorphic, most commonly granitic, rocks, which are primarily composed of quartz and feldspar (called 'grus' as a sand).
In 1978, the presence of haematopoietic stem cells is discovered in human cord blood cells. It was in 1981 when scientists Martin Evans, Matthew Kaufman and Gail R. Martin were able to derive embryonic stem cells (this term is attributed to Martin) out of the inner cell mass of a mouseâs blastocyst.
Researchers may have surmounted a decades-long biology hurdle. In the May 15 Cell online, scientists led by senior author Shoukhrat Mitalipov of Oregon Health and Science University in Portland report the first successful generation of human embryonic stem cells via somatic cell nuclear transfer.